1 Field of the Invention
This invention relates generally to a seal assembly for providing a seal between a lug and cutting cone of a rotary earth bit.
2. Description of the Related Art
An earth bit is commonly used to bore holes into a formation. Such holes may be bored for many different reasons, such as drilling for oil, minerals and geothermal steam. There are several different types of earth bits that are used to bore holes. One type is a rotary earth bit and, in a typical setup, it includes three cutting cones rotatably mounted to a corresponding lug. The lugs are connected together to form an earth bit body and, as the earth bit body is rotated in the bore hole, the cutting cones rotate in response to contacting the formation.
In normal use, the earth bit contacts rock formations while being exposed to extreme conditions, such as high temperatures and pressures. As a result, the earth bit tends to wear down. A journal segment of the lug is especially prone to wearing down because of friction between the journal segment and corresponding cutting cone. Lubricant is typically retained, with an earth bit seal, between the lug and cutting cone to reduce the friction between the lug and cutting cone. The earth bit seal also restricts the flow of debris to the region between the lug and cutting cone, which reduces the friction between them. Retaining lubricant between the lug and cutting cone, as well as keeping debris from between the lug and cutting cone, increases the life of the earth bit.
The earth bit seal is generally in rotating contact with the lug and/or cutting cone. The surface portion of the earth bit seal in rotating contact with the lug or cutting cone is known as a dynamic sealing surface. The earth bit seal and cutting cone form a dynamic seal when the earth bit seal and cutting cone are in rotating contact with each other. Further, the earth bit seal and lug form a dynamic seal when the earth bit seal and lug are in rotating contact with each other. The surface portion of the earth bit seal in non-rotating contact with the earth bit lug or cutting cone is known as a static sealing surface. The earth bit seal and cutting cone form a static seal when the earth bit seal and cutting cone are in non-rotating contact with each other. Further, the earth bit seal and lug form a static seal when the earth bit seal and lug are in non-rotating contact with each other.
Example of various types of earth bit seals are disclosed in U.S. Pat. Nos. 7,347,290, 7,188,691, 7,392,862, 7,000,712, 6,837,317, 6,695,079, 6,679,342, 6,431,293, 6,196,339, 6,033,117, 6,513,607, 6,305,483, 6,254,275, 6,176,331, 6,123,337, 5,586,611, 5,570,750, 5,009,519, 4,762,189, 5,005,989, 4,753,303, 4,516,641, as well as in U.S. Patent Application No. 20080041634.
One type of earth bit seal includes an elastomeric sealing ring, such as an O-ring seal. The elastomeric sealing ring typically experiences the extreme conditions mentioned above, which can cause it to become impregnated with debris, especially if the elastomeric sealing ring forms a part of the dynamic seal. An elastomeric sealing ring impregnated with debris is more likely to tear and lose elastomeric material, which inhibits its ability to form a seal. Further, an elastomeric sealing ring impregnated with debris operates as an abrasive ring which can undesirably remove material from the lug or cutting cone it is dynamically sealed with. A groove in the lug or cutting cone is often formed in response to the material being removed from the lug or cutting cone by an elastomeric sealing ring impregnated with debris. It is more difficult for the elastomeric sealing ring to provide a seal between the lug or cutting cone if a groove is undesirably formed in the lug or cutting cone.
Another type of earth bit seal includes a metal face seal engaged with an elastomeric sealing ring. In a typical setup, the metal face seal dynamically engages a surface of either the lug or cutting cone, or another metal face seal. Further, a static seal is typically formed between the metal face seal and elastomeric sealing ring. The metal face seal protects the elastomeric sealing ring from becoming impregnated with debris. Hence, the metal face seal reduces the amount of elastomeric material removed from the elastomeric sealing ring. The metal face seal does not become impregnated with debris as easily as seals which include elastomeric materials. Hence, the metal face seal is less likely to operate as an abrasive ring and remove material from the cutting cone or lug it is dynamically sealed with.
It is known that the cutting cone experiences a certain amount of torque in response to engaging the formation. The torque experienced by the cutting cone in response to engaging the formation causes the tip of the cone to rotate downwardly and outwardly relative to the lug. The amount of torque experienced by the cutting cone in response to engaging the formation is increased in response to seating the cutting cone further away from a rear portion of the lug. Further, the amount of torque experienced by the cutting cone in response to engaging the formation is reduced in response to seating the cutting cone closer to the rear portion of the lug. The cutting cone can be seated closer to the rear portion of the lug by reducing the amount of axial space occupied by the earth bit seal. Hence, it is desirable to provide a seal assembly which occupies a smaller amount of axial space.